The present invention relates to a combined emergency and handbrake control system for use on a light rail vehicle, and more particularly, a mass transit or rapid transit car. Braking systems for these vehicles have in recent years adopted a spring-applied brake motor for emergency and handbrake use. The spring motor provides a redundant "fail-safe" mode of operation that will insure a friction brake application even if the control system is entirely inoperative. Likewise, the spring-applied brake is useful as a parking or handbrake since it retains its braking capability even when the control system is disconnected or inoperative. If each individual car carries a self-contained brake system, the spring-applied brake will still be operative when all pneumatic pressure or hydraulic pressure has left the system. Likewise, if the vehicle is part of a train of vehicles employing a single compressor, the brake system will still be effective even when the car is disconnected from its source of pneumatic pressure.
The prior art systems for using spring-applied brakes have normally employed a separate control system to actuate a pneumatic or hydraulic motor which restrains a spring motor. In the case of a pneumatic spring-applied booster, a separate control system and a control valve is required. In the case of a separate hydraulically restrained spring motor, a separate booster or pneumatic to hydraulic convertor has been required.
The present invention obviates the need for a separate pneumatic or hydraulic control system to restrain the spring motor.